The Hong Kong government has maintained its stance in an appellate court that the now-suspended anti-mask law is in line with the Basic Law and also necessary, saying the city is still confronted with threats to public safety posed by masked protesters.

The government made the remarks on Thursday in its appeal against the High Court's ruling that the ban is unconstitutional and contravenes the constitutional document of the special administrative region. The court also ruled against the necessity of the ban on facial coverings during assemblies and protests.

Barrister Benjamin Yu Yuk-hoi, who represented the Department of Justice, said the anti-mask law was a "proportional" response to the state of affairs in the city. The seven-month-long social unrest has shown no sign of letting up, as people broke the law in Tseung Kwan O just the previous night, Yu added, referring to an assembly on Wednesday that culminated in blocking of roads and clashes with police.

Facial coverings help offenders act with impunity and also embolden them to join in violent activities, said Yu.

Masks worn by protesters could resist tear gas and pepper spray deployed by police in dispersal operations. Yu said that the anti-mask law would act as a deterrent to protesters if it came back into effect.

The mask ban was introduced on Oct 4 by Chief Executive Carrie Lam Cheng Yuet-ngor who invoked the Emergency Regulations Ordinance to stop rampant protest violence. On Nov 18, the High Court ruled that the government move was unconstitutional. On Dec 10, the court rejected the government's request to suspend the ruling, thus the ban has been lifted.

The emergency law has been in place long before Hong Kong's return to the motherland in 1997 and has been invoked several times, Yu said. It has been reviewed by the Legislative Affairs Commission of the National People's Congress Standing Committee before 1997, he added.

According to Article 8 of the Basic Law, all laws previously in force in Hong Kong shall be maintained after its return to the motherland, except for any that contravenes the Basic Law, and is subject to any amendments by the legislature of the HKSAR.

Yu also pointed out that there had always been a practical need to have this law in force during times of social unrest.

Police arrested 632 people from Oct 5 to Nov 14 for offenses under the mask ban.

In a column on Wednesday, former Court of Final Appeal Judge Henry Litton said the ruling against the anti-mask law was "catastrophic" for Hong Kong. The Department of Justice and the police, overwhelmed by the number of arrests, often had trouble identifying those arrested because their faces were covered. Moreover, suspects were released after being detained for 48 hours.